Parent for trackers with python script
Much simpler without operators, using API methods

import bpy

context = bpy.context
scene = context.scene
for o in context.selected_objects:
    # create an empty
    empty = bpy.data.objects.new("%sEmptyParent" % o.name, None)
    empty.empty_draw_type = 'CUBE'
    empty.empty_draw_size = 0.15
    # link to scene
    scene.objects.link(empty)
    # make object parent
    empty.location = o.location
    o.location = (0, 0, 0)
    o.parent = empty


All transforms (loc, rot and scale)

    # make object parent
    empty.matrix_world = o.matrix_world
    o.matrix_world = Matrix.Identity(4)
    o.parent = empty